The present invention generally relates to an optical assembly and, in particular, relates to one such assembly having means for selecting different optical fields of view and means for magnetically signalling the viewer which of the different optical fields of view is selected.
There are many optical assemblies wherein it is highly desirable and advantageous to have more than one optical field of view available to the operator. Under many such some circumstances however, it is then critical that the operator correctly and reliably know exactly which optical field of view has been selected.
Quite often however, such circumstances are usually accompanied by other difficulties as well. For example, one such circumstance may be a battlefield. Under battlefield conditions it is highly advantageous to have an optical sight that has both a wide field of view and a narrow field of view available to the user. For example, it is quite advantageous for a gunner to be able to select a target over a wide range of distances. Hence, an optical sight having one set of optical elements having a wide field of view, for relatively closer range targets and a second set of optical elements which, when positioned in the optical path of the first set of optical elements, presents a narrow field of view, for relatively distant targets, provides a gunner with the ability to select, track and/or attack targets over a large tactical battlefield. It follows, naturally, that for such an optical assembly to be effective it is critical that the operator of the sight must know which optical field of view is in use when a target is being selected. Conventionally, this is accomplished by sophisticated electronic circuitry. However, under modern battlefield conditions, it must be anticipated that all equipment in the field will be subjected to potentially damaging and interfering forms of electromagnetic energy interference (EMI) and radio frequency energy interference (RFI). Such energy interference is known to interfere with electronic circuitry to the end that either the circuitry becomes unreliable or ceases to function. At best, either of these conditions render the advantages of a multiple field of view optical assembly ineffective. In the worst case, such energy interference can cause the electronic circuitry to yield erroneous outputs, thereby causing the user to misjudge the distance to a target, i.e., the user may aim far beyond a close target if an erroneous signal indicates that the telescope path is being used.
Consequently, it is highly desirable to provide an optical assembly that not only is capable of presenting the viewer with different optical fields of view but also provides a reliable indication to the viewer as to which field of view is currently in use regardless of the presence of EMI or RFI.